Mandrel for forming insulator casing



Jan. 19, 1965 J. T. JACKSON 3,165,789

MANDREL FOR FORMING INSULATOR CASING Filed Aug. 8, 1963 4 Sheets-Sheet 1INVENTOR.

JOf-IN T. JACKSON BY WW A T TORNE YS Jan. 19, 1965 J." T. JACKSON3,165,789

MANDREL FOR FORMING INSULATOR CASING Filed Aug. 8, 1963 4 Sheets-Sheet 2J, I 1 I8 I8 I8 0 23 I5 .36.--,:'. --2.-'36.= l I?) 35 35 I6 FIG.5

INVENTOR. JOHN T. JACKSON ATTORNEYS Jan. 19, 1965 J. T. JACKSON3,155,789

MANDREL FOR FORMING INSULATOR CASING Filed Aug. 8, 1963 4 Sheets-Sheet 5FIG. IO

INVENTOR. JOHN T. JACKSON BY Mq ATTORNEYS Jan. 19, 1965 J. T. JACKSONMANDREL. FOR FORMING INSULATOR CASING 4 Sheets-Sheet 4 Filed Aug. 8,1963 INVENTOR. F IG I I JOHN T. JACKSON ATTORNEYS United States Patent3,165,739 MANDREL FOR FQRM If: INSULATGR CASING John '1'. Jackson,Louisville, Ohio, assignor to Mandrels, lnc., Louisville, Ghie, acorporation of Ohio Filed Aug. 8, 19%, filer. No. 306,739 12 Claims.(Cl. 18-45) This invention relates generally to mandrels on which hollowshells or casings are formed, and more particularly to a hollow mandrelof destructible material which can be broken up and removed after theshell has been formed thereon.

Such mandrels are frequently used to form relatively thin insulatorcasings for fuel in guided missiles, the casings being normally formedby winding filaments of elastomeric material, such as fiberglass, on themandrel.

The hollow mandrels are usually cast from frangible plaster-likematerial which must be strong and lightweight material capable ofmaintaining an extremely accurate outer surface as the filaments arewound under tension thereon, producing inward pressure on the mandrel.

fter the shell has been wound and cured, the mandrel must be broken upand removed through one or more of the ports normally provided in oneend of the case, and this must be done without damaging or distortingthe thin outer casing.

Since the hollow mandrel must have a solid wall of substantial thicknessand density in order to have adequate strength during the windingoperation, the subsequent breaking up of the mandrel requirespainstakingly careful chiseling throughout the entire mandrel to breakit into pieces which can be removed through a port hole, and

t the same time not damage orin any way detract from the contouraccuracy of the outer shell.

US. Patent No. 3,083,409, dated April 2, 1963, shows a hollow mandrelconstruction having a wall of plaster material supported on a cardboardcore, which may be a solid laminated core .or a hollow tubular core. Ineither case, plaster disks mounted on a central shaft support the outerplaster wall of the mandrel. Such a mandrel is not only expensive tobuild, but is diflicult to break up and remove because, after the shaft,core and disks have been removed, theintact outer plaster wall of themandrel must be carefully chiseled, broken up and removed. 7

It is an object of the present invention to provide an improved hollowdestructible mandrel which provides adequate strength and accuracy ofouter contour for winding an insulator casing thereon, and which issubsequently easily broken up and removed Without damaging the insulatorcasing.

More specifically, it is an object to provide ahollow mandrel having aninwardly removable keystone rib construction embedded in its outer wall.

Another object is to provide removable means interiorly of the outerwall of the mandrel for temporarily supporting the embedded keystoneribs.

A further object is to provide in one form of the invention an interiorcollapsible spoke construction for temporarily supporting theembedded'keystone ribs.

These and other objects are accomplished by the parts,

constructions and arrangements comprising the present invention,preferred embodiments of which are shown by way of example in theaccompanying drawings and ,described in detail herein. Variations indetails of construction and modifications are included within the scopeof the appended claims.

In general terms, the improved mandrel is a hollow casting'ofplaster-like material having an outer wall of extremely accuratepredetermined outer contour with longitudinally extending ribs ofkeystone or dovetail cross section embedded in the wall and adapted forrapidly inward removal therefrom, there being removable internalsupporting means in the mandrel temporarily sup- FIG. 3.

FIG. 5 is a longitudinal sectional View on line 55 of 1 FIG. 1.

FIG. 6 is a plan elevation on line 66 of FIG. 3, showing the template inposition for finishing the outer contour.

FIG. 7 is a cross section of the mandrel with the shell wound thereon.

FIG. 8 is a similar view with the keystone ribs removed.

FIG; 9 is a longitudinal plan sectional view of another embodiment ofthe improved mandrel with the template in position for finishing theouter contour.

FIG. 10 is a similar view showing the outer shell Wound thereon.

FIG. 11 is a cross sectional view on line i11l of FIG. 19.

FIG. 12 is a view similar to FIG. inner supporting shell removed.

FIG. 13 is a cross sectional view on line l313 of FIG. 12.

The mold for casting the hollow mandrel may be of any 10, showing thesuitable material and one-half of the mold is shown schematically at 15in FIGS. 1, 2 and 5. Preferably, the mold cavity 16 is formed of anysuitable material, such as a resin or reinforced fiberglass which may becoated or trade name of Ultracal has been found satisfactory.

The plaster in a semi-liquid plastic state is formed into the moldcavity by hand win any usual manner, the wall thickness being on theorder of about 2 inches, but varied according to requirements. Themandrel as cast is slightly undersize with respect to the finishedmandrel.

Whenthe wet plaster is being spread over the mold cavity in each half,longitudinally aligned .ribs 18 are embedded in the wall being formed,the ribs being keystone or dovetail in shape in cross section, with theinner V lateral dimension being the wider. The ribs preferably aremetal, wood or plastic material but may be of any suitable rigid orsubstantially rigid material.

As shown in FIGS. 1 and 5, each half mandrel is substantiallybathtub-like in shape and the rib portions 20 at the ends are curved toconform-to the curved ends 21 of The ribs 18, 2% may be continuous fromthe mandrel. end to end, or may be interrupted as shown to form alongitudinal series.' Preferably, a plurality of circumferentiallyspaced longitudinal ribs or longitudinal rib.

series is provided in each half of the mandrel. For

example, two rib series are shown in each half.

Patented Jan. 19, 1965 a) through the mandrel with its ends fitting inaligned re cesses 23 in the ends of the mold, and the shaft 22 ispositioned in the bottom half of the mold when the half mandrel 17 iscast therein.

The other or mating half of the mold and the cast half mandrel thereinwith embedded ribs are then inverted over and mated with the mold half15, and after the half mandrels have been joined with wet plastermaterial, the upper mold half may be removed as shown in FIG. 2, leavingthe upper half 17' of the mandrel mated with the lower half 17. Eitheror both of the mandrel halves may have one or more port holes formedtherein, as required.

The internal supporting means for the ribs 18, and 18', 20 arepreferably metal spoke rods 26 and 26' arranged at longitudinalintervals, with the inner end of each rod abutting the shaft and theouter end abutting a portion of the ribs.

The metal spoke rods 26 are easily positioned between the shaft 22 andthe ribs 18 when the half mandrel 17v has been cast, as illustrated inFIGS. 1 and 5, the rods being held in place by globs of web plaster andfibrous material such as hemp applied to the ends of the rods. The spokerods 26' are preferably inserted after the mandrel halves have beenmated and joined, access holes through the mold and mandrel permittingthis to be accomplished. If necessary, these holes may be filled in withplaster or like material after the rods are positioned in the mandrel.

The internally supported ribs 18 act to reinforce the wall of themandrel, giving it additional strength to withstand the pressuresexerted when the outer shell is wound thereon.

After the joint between the two cast man-drel halves 17 and 17 has set,the ends of the shaft are attached to a hoist and the mandrel lifted outof mold half 15 and mounted for rotation in a lathe indicated generallyat 27 in FIGS. 3 and 6. The shaft 22 is journaled in bearings 28 orcentered on live or dead centers and operatively connected to a motordrive 30. A side table 31 on the lathe supports a template 32 having thepredetermined contour of the finished mandrel which may be about inchlarger than the outer contour of the mandrel 17 as cast.

As the mandrel is rotated, additional wet plaster material is appliedbetween the mandrel and the template 32 which acts as a screed board toapply a skin or coating 33 of the plaster uniformly over the mandrel.Preferably, the coating is built up in several stages by setting thetemplate close to the mandrel and progressively moving it farther awaythereform. By this method an accurate outer circumference is formed onthe mandrel within a tolerance of .002 to .005 inch.

After the coating has set, the elastomeric material such as fiberglassmay be wound on the mandrel in a usual and well-known manner to form aninsulator casing or shell 34 of the required thickness. When the shellhas been cured, the operation of breaking up and removing the mandrelcomprises reaching into the mandrel through a port hole and knocking outthe spokes 26 and 26', which is very easily done since their ends areattached only by globs of plaster. Once the spokes are removed, thesnaft 22 may be pulled and the ribs or rib portions 18 and 20 are easilydislodged due to their keystone shape, and this leaves the outer wall 17in spaced-apart arcuate sections, as indicated in FIG. 8, which areeasily dislodged and broken up. To aid in dislodging the arcuate wallsections, anchor channels 35 may be embedded therein at intervals duringthe casting process, the channels having pull bars 36 attached theretoext-ending radially inward therefrom, preferably with perforate innerends, providing projections to engage for prying or pulling the wallsections loose.

The embodiment of the invention shown in FIGS. 9 to 13, inclusive,comprises a generally conical shape of mandrel which is formed and castaround the outer surface of a substantially conical tubular metal mold.Referring to FIGS. 9 and 10, the conical inner mold has a chucking block141 at its small end in which an arbor 142 is mounted axially of themold. At its large end the mold has an inner mounting ring 143 to whichthe inner plate 144 of a dome head 145 is detachably secured by screws146. An axial shaft 147 is secured in dome 145 and plate 144. The shaftand arbor provide means for rotatably mounting the mold in a lathe orthe like.

Wet plaster material to form the mandrel is applied to the outer surfaceof the mold 140 and a series of longitudinally spaced, longitudinallyextending, rigid ribs 148 embedded in the plaster. As shown in FIG. 11,four equally spaced ribs may be used, and the ribs are keystone ordove-tail shape in cross section. The ribs 148 may be attached atlongitudinal intervals to the mold by screws 149. In this embodiment,the outer contour of the ribs may be notched at longitudinal intervals,as indicated at 159, and the notches are designed to register withcircumferential grooves which are to be formed in the outer surface ofthe mandrel.

After the plaster has been rough formed into a mandrel 151 ha ing agirth or outer dimension slightly less than the required finished outercontour, including a plaster wall 152 over the dome 1.45, a templateboard 153 having projections 154 registering with the notches is mountedalongside the mandrel and used to screed on a finishing coat of plaster155 as the mandrel is rotated, forming the required accurate outercontour within a tolerance of .002 to .005 inch.

When the coating has set, the elastomeric material may be wound on themandrel to form the shell 156, which in this embodiment is required tobe substantially thicker than the shell 34, the winding preferably beingapplied over both ends of the mandrel. After the shell has been cured,the dome may be severed by a rotary cutter 157, as indicatedschematically in FIG. 10, and removed from the mandrel, whereupon thescrews 149 are removed and the mold 140 is pulled axially out of themandrel. Eyebolts 158 may then be screwed into the holes left by screws149 and used as means to aid in dislodging the ribs 148 from themandrel, leaving the outer wall in arcuate spaced-apart sections whichare then dislodged and broken up.

To facilitate removing the arcuate sections of the mandrel, it may bedesirable to mold anchor channel sections 160 into the wall 151 betweenthe ribs 148 and to hinge pull bars 161 thereon. These bars 161 lie flatin the channels against the mold 140, as shown in F168. 9 and 10, andwhen the mold is removed they are swung radially inward as shown inFIGS. 11-13 to provide projections to be engaged for prying or pullingthe arcuate mandrel sections loose.

In both embodiments, the novel mandrel provides a reinforcedconstruction of increased strength with an accurate outer contour withinthe required close tolerance, and after the outer elastomeric shell isformed thereon, the mandrel is easily broken up and removed withoutdamaging or distorting the shell in any way.

What is claimed is:

1. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, reinforcing ribs extending longitudinally of themandrel axis detachably embedded in said outer wall and each having akeystone cross sectional shape with the inner lateral dimension widerthan the outer lateral dimension, and internal means removablysupporting said ribs.

2. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, laterally spaced substantially rigid reinforcingribs extending longitudinally of the mandrel axis detachably embedded insaid outer wall, said ribs having a cross sectional shape adapted forradially inward removal of said ribs from said wall, and internal meansremovably supporting said ribs.

3. A hollow mandrel for forming a shell having an accurate, outercontour, said mandrel having a center axis and an outer wall offrangible material, reinforcing ribs extending longitudinally of themandrel axis detachably embedded in said outer wall and each having akeystone cross sectional shape with the inner lateral dimension Widerthan the outer lateral dimension, internal means removably supportingsaid ribs, and anchor means embedded in said wall between said ribs andhaving projections extending inwardly of said wall to aid in pryingloose the wall sections between said ribs.

4. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, laterally spaced substantially rigid reinforcingribs extending longitudinally of the mandrel axis detachably'embedded insaid outer wall, said ribs having a cross sectional shape adapted forradially inward removal of said ribs from said wall, internal meansremovably supporting said ribs, and anchor means embedded in said wallbetween said ribs and having projections extending inwardly of said wallto aid in prying loose the wall sections between said ribs.

5. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, reinforcing ribs extending longitudinally of themandrel axis detachably embedded in said outer wall and each having akeystone cross sectional shape with the inner lateral. dimension widerthan the outer lateral dimension, an axial shaft in the mandrel, andspoke rods detachably interposed between said shaft and said ribs forremovably supporting said ribs.

6. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, laterally spaced substantially rigid reinforcingribs extending longitudinally of the mandrel axis detachably embedded insaid outer wall, said ribs having a cross sectional shape adapted forradially inward removal of said n'bs from said wall, an axial shaft inthe mandrel, and spoke rods detachably interposed between said shaft andsaid ribs for removably supporting said ribs.

7. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a centeraxis and 'an outer wall offrangible material, reinforcing ribs extending longitudinally of themandrel axis detachably embedded in said outer wall and each having akeystone cross sectional shape with the inner lateral dimension widerthan the outer lateral dimension, an axial shaft in the mandrel, spokerods detachably interposed between said shaft and said ribs forremovably supporting said ribs, and anchor means embedded in said wallbetween said ribs and having projections extending inwardly of said wallto aid in prying loose the wall sections between said ribs.

8. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, laterally spaced substantially rigid reinforcingribs extending longitudinally of the mandrel axis detachably embedded insaid outer wall, said ribs having a cross sectional shape adapted forradially inward removal of said ribs from said wall, an axial shaft inthe mandrel, spoke rods detachably inter posed between said shaft andsaid ribs for removably supporting said ribs, and anchor means embeddedin said- Wall between said ribs and having projections extendinginwardly of said wall to aid in prying loose the wall sections betweensaid ribs.

9. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, reinforcing ribs extending longitudinally of themandrel axis detachably embedded in said outer wall and each having akeystone cross sectional shape with the inner lateral dimension widerthan the outer lateral dimension, and a tubular internal mold withinsaid mandrel axially removable therefrom and detachably supporting saidribs.

10. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, laterally spaced substantially rigid reinforcingribs extending longitudinally of the mandrel axis detachably embedded insaid outer wall, said ribs having a cross sectional shaped adapted forradially inward removal of said ribs from said wall, and a tubularinternal mold within said mandrel axially removable therefrom anddetachably supporting said ribs.

11. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, reinforcing ribs extending longitudinally of themandrel axis detachably embedded in said outer wall and each having akeystone crOSs sectional shape with the inner lateral dimension widerthan the outer lateral dimension, a tubular internal mold within saidmandrel axially removable therefrom and detaehably supporting said ribs,and anchor means embedded in said wall between said ribs and havingprojections hinged thereon for extending inwardly of said wall when saidmold is removed.

12. A hollow mandrel for forming a shell having an accurate outercontour, said mandrel having a center axis and an outer wall offrangible material, laterally spaced substantially rigid reinforcingribs extending longitudinally of the mandrel axis detachably embedded insaid outer Wall, said ribs having a cross sectional shaped adapted forradially inward removal of said ribs from said wall, a tubular internalmoldvwithin said mandrel axially removable therefrom and detachablysupporting said ribs, and anchor means embedded in said wall betweensaid ribs and having projections hinged thereon for extending inwardlyof said wall when said mold is removed.

References Cited by the Examiner UNITED STATES PATENTS 855,174 7 5/07Henry 25-l28 895,904 8/08 Smyth et al. 1,312,157 8/19 Buente 251282,303,303 11/42 Schleicher 264-66 3,030,687 4/62 Muspratt 251283,083,409 4/ 63 Crawford et al 18-45 WILLIAM J. STEPHENSON, PrimaryExaminer,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,165,789 January 19, 1965 John T Jackson It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 1, line 72, for "rapidly" read radially column 6, line 23, for"shaped" read shape Signed and sealed this 13th day of July 1965 (SEAL)Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A HOLLOW MANDREL FOR FORMING A SHELL HAVING AN ACCURATE OUTERCONTOUR, SAID MANDREL HAVING A CENTER AXIS AND AN OUTER WALL OFFRANGIBLE MATERIAL, REINFORCING RIBS EXTENDING LONGITUDINALLY OF THEMANDREL AXIS DETACHABLY EMBEDDED IN SAID OUTER WALL AND EACH HAVING AKEYSTONE CROSS SECTIONAL SHAPE WITH THE INNER LATERAL DIMENSION WIDERTHAN THE OUTER LATERAL DIMENSION, AN INTERNAL MEANS REMOVABLY SUPPORTINGSAID RIBS.